Paleoanthropologist Lee Berger, who with his 9-year-old son discovered a new hominid species, Australopithecus sediba, holds a replica of a cranium fossil in his office at the University of the Witwatersrand in Johannesburg. He uses Google Earth to seek fossil sites, and promotes his findings on Facebook and Twitter.

(Erin Conway-Smith)

Paleoanthropologist Lee Berger, who with his 9-year-old son discovered a new hominid species, Australopithecus sediba, holds a replica of a cranium fossil in his office at the University of the Witwatersrand in Johannesburg. He uses Google Earth to seek fossil sites, and promotes his findings on Facebook and Twitter.

Lee Berger’s ambitions are nothing less than revolutionary. His fossil discoveries, he says, will rewrite the science on the origins of humans, overturning 40 years of accepted theory about where we came from and how we evolved.

From anyone else, it might be an idle boast. But the U.S.-born paleoanthropologist, digging in South African caves, has already found sensational proof of an early hominid that could be a crucial long-sought transitional species in the human family tree. Now, his team of about 100 scientists, one of the world’s biggest, is preparing to search for more revelations this fall.

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Even more provocative, however, is how Mr. Berger is doing it. He believes in open access: When he excavates his fossils, the world will soon be able to watch him in a special laboratory at his dig site, in real time, on the Internet. It’s a deliberate challenge to the methods of his predecessors.

“Scientists have been notorious for hiding fossils,” he says. “They find something and hide it for 10 years while it belongs to the discoverers.”

His generation, he says, is the “Facebook generation” of scientists, who grew up with the Internet and know that the value of information is built from free exchange in a large community. “This is probably the first big discovery by a generation of scientists who’ve never been without a computer,” he says. “We’re having a ton of fun.”

Mr. Berger, now a South African citizen and a National Geographic explorer-in-residence, is a charismatic 47-year-old showman in the Indiana Jones mould, with a love of technology. He uses Google Earth to track down the most likely fossil sites. He uses Facebook and Twitter to promote his findings. He’s giving away dozens of casts of his skeleton discoveries to museums around the world. He writes books for children. He’s even encouraging the sale of merchandise, such as necklaces and earrings, with miniature versions of his fossils, as a job-creation scheme.

His research has sparked controversy. While some observers see his species discovery as the “missing link” between small-brained hominids and modern humans – the holy grail of paleoanthropology – others have dismissed it as a dead branch on the evolutionary tree. It’s a debate that might yet be settled by the next wave of research at his site.

Mr. Berger’s most crucial discoveries began in 2008 in the hilly scrub land and abandoned limestone mines northwest of Johannesburg, in an area known as the “Cradle of Humankind.” Using satellite images from Google Earth, he had identified small pits and caves where fossils might be preserved. He was poking around a pit called Malapa on Aug. 15, 2008, when his nine-year-old son spotted an intriguing fossil. Over the next few days, his team found well-preserved chunks of hominid skeletons that were later dated at nearly two million years old.

“You can imagine our excitement,” said Job Kibii, a Kenyan scientist who was on the dig team. “We knew everything would change after that.”

The full significance of those skeletons – the most complete of their kind found to date – soon grabbed the scholarly spotlight. The details have poured out in 15 scientific papers over the past three years. The Berger team identified the skeletons as a new species, which they named Australopithecus sediba. The word “sediba” means “wellspring” in the local Sotho language – a reference to how the newfound species could be a key ancestor of the human line.

The latest papers, published this year, portray the new species as a transitional “mosaic” creature – a bizarre and fascinating combination of humanlike and apelike features.

The long arms of the sediba skeletons suggested they were built for climbing trees, and their relatively small brains were not much bigger than a chimpanzee’s. Yet, their hands, like those of humans, were capable of precise gripping of tools. Their small teeth seemed human. And their feet and leg bones suggested that they walked upright for long distances, although with an awkward shuffle.

Most scientists have believed that humans had evolved in East Africa. The most famous fossil, a short upright-walking hominid known as Lucy, was discovered in Ethiopia in 1974 and was about 3.2 million years old. But Mr. Berger has boldly challenged the East Africa theory, observing that Lucy and other fossils are fragmentary, compared with the more complete skeletons of his discoveries.

“It has been traditionally a science of fragments, and this is what causes many of the wars in our science,” he says. “You can see the potential for error, because it requires an ever-growing list of assumptions. You can’t take a mandible and tell what the rest of an animal looks like. It’s a dangerous game.”

Talking excitedly to visitors at a Johannesburg museum, he points to a sediba skeleton. “This fossil is literally transforming the field of paleoanthropology,” he tells them. “You’re going to see a tremendous transformation as these skeletons are analyzed. We’ll have to rewrite all the textbooks.”

Some scientists, however, are still skeptical, and there is a subtext of resentment of Mr. Berger’s media-savvy sound bites and his talent for generating publicity. Donald Johanson, the paleoanthropologist who discovered the Lucy skeleton in 1974, has publicly suggested that the sediba species was probably just a “dead-end branch on our tree.” He said Mr. Berger is trying to sweep the East Africa evidence “under the rug.” Others have described sediba as “a failed experiment” or “an evolutionary bridge to nowhere.”

None of this worries Mr. Berger, who is convinced he will find more proof of the significance of sediba. “Perhaps it’s just what it appears to be: a transitional ancestor of our direct ancestor, Homo erectus.”

His discoveries suggest that human evolution was not a simple “march of progress” from shambling tree-climber to upright human. Rather than a chain or a tree, he says, a more accurate metaphor for human evolution is a braided stream, fed by a diversity of species that eventually led to modern humans.

Regardless of which theory is eventually proven, Mr. Berger knows the significance of what he found. “These are probably the rarest sought-after objects on the planet. As a career scientist, you dream of something like this. It changed everything about my life.”

And while he watches the preparations for the laboratory where he will unearth his fossils live on the Internet, he defends himself against the “showman” accusation. Dense academic language has made it easy for science to lose the battle for public opinion when they clash with anti-intellectual politicians, he says.

“I think too many scientists think that public communication is a dirty word. We need to train that out of them.”